A distance-measuring device for motor vehicles has been described in German Patent Application No. DE 34 20 004 A1, where the delay time of ultrasonic signals is measured using two transmitting and receiving sensors, when the ultrasonic signals are reflected off of an obstacle. In this device, two methods are used to differentiate whether the reflected signal is received from the same or from another ultrasonic sensor. On the one hand, switching over from one sensor to the other is a relatively costly procedure. On the other hand, a functional control can, in fact, be carried out in this manner, but the sensitivity of the sensors is not tested. Another problem consists in that the delay time of the measured ultrasonic signal is dependent upon sound propagation in the environment. However, the speed of propagation is dependent upon temperature, so that given a changing temperature of the ambient air, one has to be prepared for a corresponding measuring error.